1. Field of the Invention
The present invention relates to an apparatus for damping various vibrations particularly applicable to an apparatus for mounting a vehicular engine on a vehicle body.
2. Description of the Prior Art
The following characteristics are generally required for vehicular engine mounting apparata:
(1) reduction of transmission of low frequency vibrations generated from a vehicular engine to a vehicle body having large amplitudes (displacements) when the engine is cranked and in an idling state or when the vehicle is abruptly started by damping such low-frequency vibrations through the apparatus;
(2) prevention of a resonance of the engine due to the receipt of large-amplitude, low-frequency vibrations transmitted to the engine through a vehicle body from a road surface which has recesses and convexes by damping the large-amplitude, low-frequency vibrations when the vehicle runs on such a rough road; and
(3) suppression of increase in noise within a vehicle compartment due to a propagation of small-amplitude, high-frequency vibrations to the vehicle compartment by damping the small-amplitude and high-frequency vibrations generated by the engine when the vehicle runs at a high speed.
A fluid-sealed type vehicular engine mounting apparatus has recently been proposed in which is incorporated a hydraulic damping mechanism acting upon a change in a height of an elastic object intervened between the engine and vehicle body. The above-described fluid-sealed type engine mounting apparatus is exemplified by a Japanese Patent Application Unexamined Open No. Sho 57-25536, published on Feb. 10, 1982.
FIG. 1 shows a conventional fluid-sealed type vehicular engine mounting apparatus.
In FIG. 1, a metal fixture a is attached to the vehicular engine via a bolt b. On the other hand, another metal fixture c is attached to a body frame constituting the vehicle body via other bolts d. A hollow rubber mount e is intervened between the metal fixtures a and c. An upper end of the rubber mount e is vulcanized and adhered to the metal fixture a and a lower end thereof is vulcanized and adhered to the metal fixture c. A partitioning plate g and diaphragm h are attached to the metal fixture c via a holding fixture f. A first chamber i.sub.1 is formed on an upper side of the partitioning plate g and a second chamber i.sub.2 `is formed on a lower side of the partitioning plate g. An operating fluid j is filled within both chambers i.sub.1 and i.sub.2.
An orifice k is penetrated through the partitioning plate g for communicating both chambers i.sub.1 and i.sub.2. The small orifice k is formed within an envelope .lambda. fixed to a substantially center part of the partitioning plate g.
The fluid-sealed type vehicular engine mounting apparatus having a structure as described above with reference to FIG. 1 damps the engine vibrations by the utilization of the orifice k when the mount rubber member e is deformed due to the engine vibrations, accordingly the volume of the first chamber i.sub.1 is changed, and the operating fluid j moves between both chambers i.sub.1 and i.sub.2 via the orifice k of the envelope .lambda..
In the conventional engine mounting apparatus which starts action of the hydraulic damping mechanism simultaneously when the height of the mount rubber member e is changed (the change in volume of the chambers i.sub.1, i.sub.2, the change in a spring constant of the mount rubber member e is proportional to the change in the damping force. Therefore, if the spring constant of the mount rubber member e is set larger so as to sufficiently damp the large-amplitude, low-frequency vibrations, the damping force becomes excessive for the small-amplitude, high-frequency vibrations so that the small-amplitude, high-frequency vibrations cannot sufficiently be damped. On the contrary, if the spring constant of the mount rubber member e is set lower so as to sufficiently damp the small-amplitude, high-frequency vibrations, the large-amplitude, low-frequency vibrations cannot sufficiently be damped.
In this way, the setting of the spring constant for the rubber mount e largely affects the capability of damping various vibrations that the engine mounting apparatus needs to have.
In addition, since pressure is generated in the sealed fluid in the hollow portion of the rubber mount e, the pressure generation affects a durability of the rubber mount e itself and the mounting apparatus itself becomes complex and large in construction.